Overground locomotion in intact rats: interlimb coordination, support patterns and support phases duration.

The interlimb coordination during overground locomotion was analysed in intact rats, using the method of contact electrodes (Górska et al. 1998). It was found that in animals moving with a speed ranging from 10 to 78 cm/s (step cycles 685 to 215 ms, respectively) the interlimb coordination was characterized by homologous phase shifts close to 0.5 and much shorter diagonal than lateral phase shifts. These features corresponded to symmetrical gait with diagonal sequence and diagonal couplets (Hildebrandt 1976). Shortening the step cycle changed the gait from a walking trot (duty factor > 0.5) into a running trot (duty factor < 0.5). Correspondingly, the support patterns in the four-legged step cycles, i.e., the sequence of phases of support on various limbs changed: the support on diagonal limbs persisted but the three-limb support was replaced by one-limb support and the support on homolateral limbs by phases of flight. For each phase of support the relationship between its absolute and relative durations and the step cycle duration is being described. The paper explains the variability of support patterns described in the literature. The picture of locomotion obtained in intact rats will be used as a template for studying locomotor control deficits after CNS lesions.

Overground locomotion in intact rats: contact electrode recording.

The aim of the experiments was to check the validity of the method of contact electrodes for studying overground locomotion in the rat. The basic indices of locomotion, obtained in 7 intact rats with at least 100 steps recorded in each, were analysed and compared with those described by other authors using different methods of movement recording. It was found that the method of contact electrodes gives reproducible and reliable results and may thus be used in further experiments of rat locomotion after CNS lesions.

Different forms of impairment of the fore-hindlimb coordination after partial spinal lesions in cats.

Effects of large low thoracic (T10-T11) partial spinal lesions involving either the ventral quadrants of the spinal cord and, to a different extent the dorsolateral funiculi, or different extent of the lateral funiculi and/or the dorsal columns, on the fore-hindlimb coordination were examined in cats walking overground at moderate speeds. In both groups of operated cats, except those in which the lesion was essentially confined to dorsal columns, three different forms of impairment of fore-hindlimb coordination were observed, depending on the extent of lesion: (1) a change of locomotion towards pacing with preservation of the equality rhythms in the fore- and the hindlimbs; (2) episodes of fore- and hindlimb rhythm dissociation and (3) a permanent dissociation of the fore- and hindlimb rhythms. A comparison of the results obtained in these two groups of operated cats points to the more important role played by the lateral funiculi, than by other parts of the spinal white matter, in controlling the fore-hindlimb coordination in cats.

Different patterns of fore-hindlimb coordination during overground locomotion in cats with ventral and lateral spinal lesions.

The effect of large, low thoracic (T10-T11), partial spinal lesions involving the ventral quadrants of the spinal cord and, to a different extent, the dorsolateral funiculi, on fore-hindlimb coordination was examined in cats walking overground at moderate speeds (40-100 cm/s). Three different forms of impairment of fore-hindlimb coordination depending on the extent of the lesions, were observed. Lesions sparing the dorsolateral or the ventral funiculus on one side preserved the equality of the fore- and hindlimb locomotor rhythms but changed the coupling between the movements of both girdles as compared to intact animals. Larger lesions in which, in addition to the ventral quadrants of the spinal cord, also major parts of the dorsolateral funiculi were destroyed elicited episodes of rhythm oscillations in both girdles, which appeared at the background of a small difference in these rhythms. Lesions destroying almost the whole spinal cord induced a permanent difference (about 200 ms) in the step cycle duration of the fore- and the hindlimbs. However, even in these animals some remnant form of fore-hindlimb coordination was found. The results suggest that dorsolateral funiculi play a major role in preserving the equality of rhythms in the fore- and the hindlimbs, while lesions of the ventral quadrants change the coupling between limbs.

Unrestrained walking in cats with medial pontine reticular lesions.

The early postoperative effects of lesions, aimed to destroy the caudal pole of the nucleus reticularis pontis oralis (NRPO) and the rostral pole of the nucleus reticularis pontis caudalis (NRPC), were tested in freely moving cats, walking at moderate speed (0.4-1.0 m/s). In cats in which these structures were partly or completely destroyed, the main effect of lesions was an impairment of fore-hindlimb coordination, as shown by a change in the relationships between the lateral and diagonal time shift durations and the step cycle duration. In the second week after the surgery the values of the slopes of linear regressions relating these variables were markedly changed as compared to the preoperative data. The results suggest that the NRPO and NRPC are involved in maintaining the proper forehindlimb coordination during unrestrained locomotion in cats.

Unrestrained walking in intact cats.

In five freely moving cats walking with speeds of 0.4-1.0 m/s several parameters of locomotion were investigated. Special attention was paid to the analysis of support patterns and the duration of support phases. The animals used almost exclusively (in 88 to 99% of steps) the 3-2-3-2-3-2-3-2 support pattern in which phases of support on three limbs alternated with phases of support on two limbs, homolateral and diagonal. The relative duration of support phases showed a tendency to decrease with increased locomotor velocity, except for the supports on diagonal limbs which slightly increased. The mean duration of the majority of support phases was similar and ranged between 12.2 and 14.5% of the step cycle. Phases of support on both hind- and one forelimb were somewhat (about 5%) shorter. It is concluded that the relative stability of support patterns and of the duration of support phases during walking observed in the present experiment may serve as a template for comparing changes in the gait produced by various CNS lesions.

Unrestrained walking in cats with partial spinal lesions.

In four cats with partial spinal lesions, performed at a low thoracic level, involving ventral quadrants and, to a different extent, the dorsolateral funiculi, several parameters of locomotion were analyzed during unrestrained walking at moderate speed (0.3-1.0 m/s). Special attention was paid to the analysis of support patterns and the durations of support phases in step cycles. The operated subjects displayed a much greater variability of support patterns than intact cats as well as changes in the relative duration of some support phases. The most striking difference was an increase in the relative duration of support on two homolateral limbs accompanied by a reduction of support on diagonal limbs. These changes were mainly due to an impairment of fore-hindlimb coordination as shown by an increase in the phase shifts between the movements of diagonal limbs. Other parameters of locomotion were essentially unaltered, except for cats in which the lesion destroyed bilaterally major portions of the dorsolateral funiculi.

Hindlimb swing, stance and step relationships during unrestrained walking in cats with lateral funicular lesion.

In freely moving cats, walking at speeds of 0.4-1.0 m/s, lesions of the lateral funiculi, performed at the low thoracic level, increased the hindlimb step cycle duration and changed the relationships between the stance and swing phase durations and the step cycle duration. The values of the slopes of linear regression lines relating the swing and the step durations were markedly increased, while those for the stance phase were decreased, compared to intact animals. Control dorsal column lesion produced no change in these parameters. The results suggest that pathways in the lateral funiculi play a substantial role in maintaining the proper structure of the step cycle.

Hindlimb muscle activity during unrestrained walking in cats with lesions of the lateral funiculi.

In freely moving intact cats and cats with bilateral lesions of the lateral funiculi the foot contact signals and the activity of selected muscles operating at the ankle and knee joints were analysed during walking at moderate speed (0.4-1.0 m/s). No essential changes in the activity of the muscles gastrocnemius lateralis (GL), semitendinosus (ST) and vastus lateralis (VL) were found in operated animals. The tibialis anterior (TA) muscle activity had a shorter duration than the swing phase in operated animals and showed an impaired coactivation with gastrocnemius lateralis (GL) muscle at the end of the swing phase. Pilot experiments indicated that these deficits may be partly compensated for by peroneal nerve electrostimulation. Analysis of regression lines relating the swing duration to the step duration, determined from EMG records, confirmed our previous results, based on foot contact signals (Górska et al. 1993), showing that in cats with lateral funicular lesions the swing duration varies much more with the step duration than in intact animals.

Multiple spike-train analysis using mutual interval matrix.

The principal-component approach is applied to the analysis of sequences of neuronal action potentials (spike trains). Multiple spike trains are represented as a sequence of vectors of mutual interspike intervals and are considered to be part of the trajectory of a dynamic system. The trajectory matrix is decomposed into a number of 'basic spike patterns' and their relative magnitudes by singular-value decomposition. The representation provides a convenient framework for analysis of dynamic relations and cooperation between neurons in an observed network. Examples of applications to simulated and cerebellar data are presented.

The methods of surface EMG analysis.

The use of surface emg as a tool for quantification is described. First, the specific advantages of the surface emg are discussed. Techniques for analysis of the emg signal which estimate and detect the action potentials of the individual motor units and estimate some global properties of muscle activity are reviewed. A survey of data on relations between the properties of motor unit action potential, the properties of motor unit activity and the results of signal processing are given.

Modelling study of spinal generators structure; the role of alpha motoneurons, Renshaw cells and Ia interneurons in locomotion.

The properties of a model system composed of nets of motoneurons, Ia interneurons and Renshaw cells corresponding to the set of muscles driving one joint were analyzed from the point of view of their participation in locomotion control, i.e., generation of signals driving individual muscles. The model was constructed of neuron-like analog elements. The relations between the structure of the system, its control by tonic and phasic inputs and the properties of the generated signals were examined. The pattern of activity of motoneuron-like elements was considered to reflect the physiological pattern of muscle activity during locomotion. The network modelled in this way was an adjustable system, i.e., the parameters of the generated pattern could be varied by both tonic and phasic signals. A phasic signal acting on a background of moderate tonic signals seemed to enable a broader adjustment of the parameters of the generated pattern than tonic signals only. The best correspondence between generated and physiological patterns was obtained when the Renshaw cells were additionally and selectively inhibited by tonic signals.

Dependence of gait pattern on the type of coupling between hind- and forelimb generators: modelling study.

Dependence of gait pattern on the way of possible coupling between fore and hindlimb girdles was investigated. This dependence was analysed using the analog model of neuronal net of spinal generator. Both nets (i.e., for fore and hind girdles) could be synchronized by any coupling between the executive and intrinsic elements. However, only few of them assured generation of patterns corresponding to physiological gaits. Patterns corresponding to walk and trot were obtained with inhibitory connections from hind intrinsic elements to fore executive ones. Pace was obtained at the coupling connections directed from hind executive elements to fore ones. To obtain gallop it was necessary to couple fore executive elements with hind ones by inhibitory connections.